This invention relates to an image processing apparatus and, more particularly, to an image processing apparatus for recording an image using a recording material (ink, toner or the like) having a plurality of color components in a color copier, color facsimile machine, etc.
When a color image is recorded by an additive mixture of color stimuli, and especially when black slender lines and characters are recorded, based upon an image signal separated into colors (R, G, B), generally recording is performed by superimposing recording materials in the three colors of Y (yellow), M (magenta) and C (cyan) or the four colors of Y, M, C and K (black).
However, when an image is recorded by superimposing these recording materials having three or four colors, the following problems arise:
1. The portion where the materials overlap do not appear perfectly black.
2. Since it is difficult to superimpose the recording materials accurately, the colors become positionally displaced and the black color does not appear. In addition, the boundary with a tone image is rendered indistinct.
3. If recording is carried out based upon pseudo-half-tone processing (such as processing based upon the dither method or error-diffusion method), for example, dots are not linearly continuous, and therefore slender black lines cannot be expressed at a high resolution.
Accordingly, in a case where an image is binarized, it has been contemplated to separate and identify black character portions or slender black-line portions from input image data and record these isolated portions using a single color, namely the color black. Though such an expedient is capable of solving the foregoing problems, there are instances where this processing comes to be applied also to the gray edges of ordinary images, thereby reducing picture quality.